In the electrical discharge machine to process the machined article (article to be machined) of metal by means of electrical discharge between the machined article and the discharging wire that is immersed in or sprayed with electrically non-conductive liquid, the tip of the discharge wire has to always be kept in a given position opposing to a discharge process region of the machined article to achieve stable electrical discharge, in order to machine the article in a desired shape. To that end, a XYZ-driving mechanism has been proposed so far, which maintains a constant discharge distance between the discharge wire and the machined article by shifting either one of them. The driving mechanism shifts either one of the discharge wire and the machined article to adjust a potential indicative of a relative position therebetween, to a predetermined value. Also, in general, a desired final shape of the machined article may rather be complicated and the distance between the discharge wire and the machined article during machining may often be approximately 10 microns or less. In this circumstance, the XYZ-driving mechanism is required to be quickly responsive to adjust the relative position for a targeted potential.
In order to satisfy with such requirement, a patent document 1, WO 02/24389 A1, discloses a process and apparatus for machining by electrically discharging with a XYZ-driving mechanism of quick response. According to this structure, if a thin tungsten wire having a diameter of approximately 0.2 mm or less is used, it may be consumed in a short time period. Also, for example, if the machined article is to be processed deeply, the discharge wire has to be fed out more, expecting that it will quickly be consumed, otherwise, the discharge wire should be fed intermittently in response to consumption thereof. However, the patent document 1 fails to disclose an automatic feeder of the thin wire. Therefore, since it takes substantial time to feed the thin, quick-consumptive wire of controlled length, the apparatus described in the patent document 1 cannot achieve the high-speed processing unless a high-speed wire feeding mechanism is incorporated therein.
Another patent document 2, JP 08-290332 A, discloses a wire feeding mechanism, in which a top portion of an electrode wire is held by a holder that is supported by a chuck provided with a main shaft of the processing apparatus. In this structure, the holder is replaced together with remained portion of the wire without being fused and consumed during electrical discharge. Also, in order to avoid frequent replacement of the wire and frequent interruption of electrical discharge caused thereby, the elongated wire having length of approximately 30 cm is used. However, since such thinner wire is less rigid and held at the top portion, such elongated wire behaves elastically and the bottom portion of the wire oscillates vertically and horizontally relative to the opposing machined article. Thus, the apparatus of the patent document 2 has a drawback, which cannot feed out the wire in a stable and reliable manner. Also, even in case where the XYZ-driving mechanism is used for driving the machined article or the wire in a quickly responsive manner, there is another drawback that such quick response would be deteriorated at the bottom portion of the wire. Therefore, the wire feeding mechanism of the patent document 2 cannot be incorporated into the electrical discharge machine of the patent document 1.
Furthermore, a patent document 3, JP 2001-038532 A, discloses another wire feeding mechanism to continuously feed the wire out of a pair of rollers. However, this mechanism also has several problems. For instance, the wire may be deformed or flattened close to the pressing region of the roller. Also, since the wire is wound around and held by a roller, thereby prohibiting the wire to be pivoted around the center axis thereof, it is difficult to machine a cylindrical hole on the article straightly without eccentricity.
In addition, a patent document 4, EP 0826455 B1, discloses another wire mechanism for centering the wire, in which the wire may be released if necessary. However, this document also fails to even suggest an automatic feeder of the wire.
Patent Document 1:WO 02/24389 A1Patent Document 2:JP 08-290332 APatent Document 3:JP 2001-038532 APatent Document 4:EP 0826455 B1